In recent years, some hybrid cars are seen running on the road in a stream of cars supplied with power only from a common internal combustion engine. The hybrid car refers to a vehicle developed for improving exhaust emission deterioration or fuel efficiency lowering involved with driving only with the internal combustion engine.
A hybrid car refers to a vehicle including a motor-generator that serves as a motor generating drive torque using electric power or as a generator, together with the internal combustion engine. Japanese Patent Laying-Open No. 11-178113 discloses adoption of a guard value when a final torque is large, the final torque being torque resulting from addition of assist torque for starting an engine and drive torque necessary for running of such a hybrid car.
Conventionally, in motor control, a final torque control value has been calculated by calculating a waveform of vibration-suppression torque for suppressing vibration such as torque ripple involved with rotation of the motor separately from a waveform of torque control for propelling a vehicle and adding these waveforms together. For such a torque control value, a guard value for motor protection has been set.
FIG. 14 is a diagram showing a waveform of the final torque control value obtained by applying the guard value.
Referring to FIG. 14, a guard value GT is applied to a torque control raw value TR based on an acceleration request from an accelerator pedal or the like operated by a driver and the resultant value is subjected to filtering processing, thereby calculating a torque filter value TRF.
Meanwhile, a waveform, obtained as a result that guard values G1, G2 for the vibration-suppression torque are applied to a raw value Y for vibration-suppression torque for mitigating torque ripple of the motor, is superimposed on torque filter value TRF. Final torque control value T is thus calculated.
Final torque control value T, however, abruptly varies at angular portions PA, PB. Therefore, follow-up characteristic of accuracy in current feedback control is deteriorated.
FIG. 15 is a waveform diagram for illustrating a state where follow-up characteristic of accuracy in current feedback control has deteriorated.
Referring to FIG. 15, in a portion where the vibration-suppression torque control value abruptly varies as shown in FIG. 15, overshoot occurs as shown with A, B and C, a current that should not originally be fed flows, and power is wasted. In addition, increase in the current may affect the life of a battery and an inverter.